Summary
Highlights
DNA is long and codes for many proteins. To get the code for a specific protein from the nucleus to the ribosomes, a smaller copy of the necessary DNA section is made through transcription. Transcription occurs in the nucleus and is the first step of protein synthesis. A portion of DNA is unzipped, and RNA polymerase uses one strand as a template to make mRNA, replacing thymine with uracil.
mRNA only copies the specific DNA portion that codes for the desired protein, which is typically a very small percentage of the entire DNA. This small section includes start and stop signals. After formation, the mRNA leaves the nucleus through a nuclear pore and enters the cytoplasm, where it will find a ribosome.
Ribosomes, made of protein and RNA, are the protein-making machines. They read the mRNA code, which is processed three bases at a time (called codons). tRNA (transfer RNA) brings the correct amino acids to the ribosome to build the protein. Each tRNA has an anticodon that matches a specific mRNA codon and carries a specific amino acid.
Translation begins when mRNA attaches to a ribosome and a start codon (usually AUG) is read. The first tRNA brings its amino acid, then subsequent tRNA molecules match their anticodons to the mRNA codons, forming peptide bonds between amino acids. The mRNA shifts, and the process continues until a stop codon is reached, at which point the protein is formed and ready to fold.
To determine the sequence of amino acids, you use an mRNA amino acid chart. By finding the first, second, and third letters of each codon on the chart, you can identify the corresponding amino acid. For example, AUG codes for methionine (the start amino acid), CCC for proline, GGC for glycine, and UAA is a stop codon, signaling the end of protein synthesis.